The DHCCP is a multicentre observational study of patients being treated for hypertension in the United Kingdom. The influence of the type of anti-hypertensive therapy on survival was examined in 2,697 patients followed from 1971 with 206 deaths up to November 1981. Patients were classified by three types of treatment after one year in the project: betablockers (1,387), methyldopa (452) and others (667), (70% on diuretics only). The data were analysed both for all patients and for a subset excluding patients with previous ischaemic heart disease by all cause and IHD age-adjusted rates and life table analysis. Men on beta blockers had lower rates for total mortality, when compared with men on methyldopa (64% of the methyldopa rate, P less than 0.05) and when compared with men on other treatments (76% of the other treatment rate, P less than 0.1). The results for IHD mortality were similar. This improved survival of men in the beta blocker group was also found in the subset with no prior history of IHD. The benefit of beta blockers was not apparent in women: the lowest rates were observed for women on methyldopa, but the confidence limits for the ratios of relative rates were wide. Adjustment for blood pressure and cigarette smoking using the Cox proportional hazards model did not substantially modify the ratios of the mortality rates for the treatment groups. A sub-group analysis showed the reduction in all cause and IHD mortality associated with beta blockers was mainly due to the effect in non-smoking men.(ABSTRACT TRUNCATED AT 250 WORDS)